The overall crystallization-rate of polyesters can be enhanced by several nucleating additives, such as minerals, salts, pigments, etc. Such heterogeneous nucleating agents may however adversely affect mechanical properties and/or polyester stability. U.S. Pat. No. 3,833,535 to Wambach et al, describes the addition of neucleating agents polyesters in column 7, lines 37 to 52.
Diamines, copolymerized into the polyesters, have been shown to nucleate crystallization more efficiently, probably because of their homogeneous molecular distribution over the polymer mass. Their nucleation mechanism has been related to association (hydrogen-bonding) in the melt of the copolymerized diamide-units, thus creating nuclei which initiate crystallization of the polyester-segments. In PBT, replacement of 5% of (non adjacent) butanediol-units by butanediamine, in other words replacing 1 of on average 20 butanediols by butanediamine, results for an injection moldable grade consisting of 100-200 units in a diamide-density of 5-10 units per polymer chain. At this density, amide--amide association via intra- and/or inter-chain hydrogen bonding is not unlikely, and has been advanced to explain nucleation of the polyester-crystallization. At higher replacement-levels, e.g. 1 butanediamine for every 10 butanediols, melting point enhancement of PBT becomes significant, obviously due to efficient reduction of the entropy-change upon melting because of the cooperativity of the amide--amide associations. See A. van Bennekom, thesis 1995 Univ. Twent (Netherlands).
EP-A-0 315 027 describes copolymers of the general formula: ##STR3##
In this formula x, y and z are each integers from 1 to 100,000. G may be the residue of tetramethylenediamine, E may be the residue of terephthalic acid, R may be the residue of 1,4-butanediol, Ar is a divalent aromatic carboxylic group. Units A comprise from about 1 to about 99 percent by weight of said copolymer and units B comprise from about 99 to about 1 percent by weight of said copolymer. Said copolymers can be block copolymers, "alternating" copolymers, or random copolymers. EP-A-0 315 027 also indicates that the block copolymers are useful in automotive applications, electrical appliances, and food wrappings, as stand alone resins, in blends with other resins such as polyesters, polyarylates and polyamides and as tie resins to bond two different resin layers.
Polyesteramide resins wherein R and G are the residue of 1,4-butanediol and E and Ar are paraphenylene radicals have been disclosed in U.S. Pat. No. 5,510,451 to Gaymans, et al. Polyesteramide as blends of polycarbonate resins and polyesteramide resins have been disclosed in U.S. Pat. No. 5,731,389 to Bailly et al. Blends of polyphenylene ether resins and polyesteramide resins have been disclosed in commonly owned and pending application U.S. Pat. No. 5,744,068 to Bailly et al.